Chapter 3 Acceleration and free fall - Light and Matter

Summary
Selected vocabulary
gravity . . . . . . A general term for the phenomenon of attraction
between things having mass. The attraction
between our planet and a human-sized object
causes the object to fall.
acceleration . . . The rate of change of velocity; the slope of the
tangent line on a v − t graph.
Notation
vo . . . . . . . . . initial velocity
vf . . . . . . . . . final velocity
a . . . . . . . . . . acceleration
g . . . . . . . . . . the acceleration of objects in free fall; the
strength of the local gravitational field
Summary
114 Chapter 3 Acceleration and free fall
Galileo showed that when air resistance is negligible all falling
bodies have the same motion regardless of mass. Moreover, their
v − t graphs are straight lines. We therefore define a quantity called
acceleration as the derivative dv/dt. This definition has the advantage
that a force with a given sign, representing its direction, always
produces an acceleration with the same sign. The acceleration of objects
in free fall varies slightly across the surface of the earth, and
greatly on other planets.
For motion with constant acceleration, the following three equations
hold:
∆x = vo∆t + 1
2 a∆t2
v 2 f = v2 o + 2a∆x
a = ∆v
∆t
They are not valid if the acceleration is changing.